scholarly journals Evolutionary Tracks for Central Stars of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 463-472 ◽  
Author(s):  
Detlef Schönberner
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Helium Burning ◽  
Hydrogen Burning ◽  
Stellar Envelope ◽  
Thermal Pulse ◽  
Pulse Cycle ◽  
Central Stars

Our understanding of the evolution of Central Stars of Planetary Nebulae (CPN) has made considerable progress during the last years. This was possible since consistent computations through the asymptotic giant branch (AGB), with thermal pulses and (in some cases) mass loss taken into account, became available (Schönberner, 1979, 1983; Kovetz and Harpaz, 1981; Harpaz and Kovetz, 1981; Iben, 1982, 1984; Wood and Faulkner, 1986). It turned out that the evolution depends very sensitively on the inital conditions on the AGB. More precisely, the evolution of an AGB remnant is a function of the phase of the thermal-pulse cycle during which this remnant was created on the tip of the AGB by the planetary-nebula (PN) formation process (Iben, 1984, 1987). This was first shown by Schönberner (1979), and then fully explored by Iben (1984). In short, two major modes of PAGB evolution to the white dwarf stage are possible, according to the two main phases of a thermally pulsing AGB star: the hydrogen-burning or helium-burning mode. If, for instance, the PN formation, i.e. the removal of the stellar envelope by mass loss, happens during a luminosity peak that follows a thermal pulse of the helium-burning shell, the remnant leaves the AGB while still burning helium as the main energy supplier (Härm and Schwarzschild, 1975). On the other hand, PN formation may also occur during the quiescent hydrogen-burning phase on the AGB, and the remnant continues then to burn mainly hydrogen on its way to becoming a white dwarf.

scholarly journals Peculiar Red Giants — What Kind of White Dwarfs do They Become?

1989 ◽  
Vol 106 ◽  
pp. 205-221 ◽  
Author(s):  
Icko Iben
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Buffer Zone ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Additional Mass ◽  
Hydrogen Burning ◽  
Thermal Pulse ◽  
Pulse Cycle ◽  
Model Star

AbstractAfter a brief commentary on the place of “peculiar red giants” in the overall scheme of stellar evolution, an outline is given of the various possibilities for post asymptotic giant branch (AGB) evolution. The behavior of a post-AGB model star is crucially dependent on where in a thermal pulse cycle the mass of the hydrogen-rich envelope is reduced to such an extent that departure from the AGB must follow on a thermal time scale. If departure from the AGB occurs while the model is still burning hydrogen, post-AGB behavior depends on the mass of the helium buffer zone (- zone containing predominantly helium which has been processed through the hydrogen-burning shell following the last thermal pulse on the AGB). If departure occurs at an arbitrary time during the hydrogen-burning phase, then: (1) in - 25% of all cases, the post-AGB model will experience a final helium shell flash, and, in consequence of additional mass loss, may become a non-DA white dwarf; (2) in - 60% of all cases, the model will cease burning hydrogen when the mass in its hydrogen-rich envelope is reduced to ∼ 10-4Mʘ and will evolve into a DA white dwarf; and (3) in - 15% of all cases, the model will experience a final hydrogen shell flash, but the outcome with regard to spectroscopic type is unclear. If departure from the AGB occurs while the model is burning helium, the result is either the same as in option (3) just described, or mass loss during the post-AGB helium-burning phase may turn the star into a non-DA white dwarf.

scholarly journals Stellar wind models of central stars of planetary nebulae

2020 ◽  
Vol 635 ◽  
pp. A173 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát ◽  
I. Krtičková
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Terminal Velocity ◽  
Asymptotic Giant Branch ◽  
Central Stars ◽  
Loss Rates

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

scholarly journals H- and He-burning Central Stars and the Evolution to White Dwarfs

2003 ◽  
Vol 209 ◽  
pp. 101-108
Author(s):  
T. Blöcker
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Evolutionary History ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Stellar Structure ◽  
Transitional Stage ◽  
Thermal Pulse ◽  
Convective Overshoot ◽  
Central Stars

The structure and evolution of central stars of planetary nebulae (CSPNe) is reviewed. CSPNe represent the rapid transitional stage between the Asymptotic Giant Branch (AGB) and the white-dwarf domain. It is shown that the whole evolution off the AGB through the central-star regime depends on the evolutionary history. The detailed evolution into a white dwarf is controlled by the internal stellar structure which, in turn, is determined by the duration of the preceding AGB evolution and therefore by the AGB mass-loss history. The evolution of hydrogen-deficient central stars has been a matter of debate since many years. Convective overshoot appears to be a key ingredient to model these objects. Various thermal-pulse scenarios with inclusion of overshoot are discussed, leading to surface abundances in general agreement with those observed for Wolf-Rayet central stars.

scholarly journals Binary Stars and Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 505-522 ◽  
Author(s):  
Icko Iben ◽  
Alexander V. Tutukov
Keyword(s):  
Neutron Star ◽  
Binary Star ◽  
Planetary Nebulae ◽  
Roche Lobe ◽  
Asymptotic Giant Branch ◽  
Close Binaries ◽  
Helium Burning ◽  
Hydrogen Burning ◽  
Common Envelope ◽  
Central Stars

A non-negligible (∼ 15–20%) fraction of planetary nebulae is expected to be formed in close binaries in which one component fills its Roche lobe after the exhaustion of hydrogen or helium at its center. The nebula is ejected as a consequence of a frictional interaction between the stellar cores and a common envelope; the ionizing component of the central binary star may be a relatively high luminosity contracting star with a degenerate CO core, burning hydrogen or helium in a shell, or it may be a lower luminosity shell hydrogen-burning star with a degenerate helium core or a core helium-burning star. Even more exotic ionizing central stars are possible. Once the initial primary has become a white dwarf or neutron star, the secondary, after exhausting central hydrogen, will also fill its Roche lobe and eject a nebular shell in a common envelope event. The secondary becomes the ionizing star in a tight orbit with its compact companion. In all, there are roughly twenty different possibilities for the make-up of binary central stars, with the ionizing component being a post asymptotic giant branch star with a hydrogen- or helium-burning shell, a CO dwarf, a core helium-burning star, a shell helium-burning star with a degenerate CO core, a shell hydrogen-burning star with a degenerate helium core, or a helium degenerate dwarf, while its companion is a main sequence star, a CO degenerate dwarf, a helium star, a helium degenerate dwarf, or a neutron star. We estimate the occurrence frequency of several of these types and comment on the prior evolutionary history of 4 observed binary central stars.

scholarly journals Evolutionary Tracks

1993 ◽  
Vol 155 ◽  
pp. 415-422 ◽  
Author(s):  
Detlef Schönberner
Keyword(s):  
White Dwarf ◽  
Formation Process ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Stellar Structure ◽  
Cycle Phase ◽  
Thermal Pulse ◽  
The Past ◽  
Pulse Cycle ◽  
Central Stars

It is now accepted without any doubts that the central stars of Planetary Nebulae (CPN) are rapidly evolving objects in the transition from the asymptotic giant branch (AGB) to the white-dwarf regime. After the pioneering study of Paczyński (1971) it has been demonstrated by Schönberner (1981) that Paczyński's calculations are too crude for the understanding of post-AGB evolution because the latter depends very sensitively on the detailed internal stellar structure, i.e. on the past AGB evolution. More precisely, the evolution of an AGB remnant is a function of the thermal-pulse cycle phase ϕ during which this remnant has been created by the planetary-nebula (PN) formation process. This has been shown by Schönberner (1979, 1983) and later fully been explored by Iben (1984).

scholarly journals Observations of Planetary Nebulae Haloes

2003 ◽  
Vol 209 ◽  
pp. 447-450
Author(s):  
Romano L.M. Corradi
Keyword(s):  
Mass Loss ◽  
Surface Brightness ◽  
Planetary Nebulae ◽  
Statistical Properties ◽  
Hydrogen Burning ◽  
Morphological Component ◽  
Loss Event ◽  
Central Stars

An improved database of ionized haloes around PNe has been built by adding the results of an extensive observational campaign to the data available in the literature. The new observations allowed us to discovered new haloes around CN 1-5, IC 2165, IC 2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, and possibly IC 1747.The global sample consists of 29 AGB haloes, that are believed to still contain information about the mass loss from the AGB progenitor star. Six of these haloes show a highly asymmetrical geometry that is tentatively ascribed to the interaction of the stellar outflow with the ISM.Another 5 PNe show candidate recombination haloes. These are produced by the recombination front that sets up when the stellar luminosity drops in its post-AGB evolution. The resulting, limb-brightened shell resembles a real AGB halo, but is not related to AGB any mass loss event.Double AGB haloes are found in at least 4 PNe.For 11 PNe, deep images are available, but no halo is found to a level of ≲ 10-3 the peak surface brightness of the inner nebula.These observations show us that ionized haloes are a common morphological component of PNe, being found in 70% of elliptical PNe for which adequately deep images exist. Statistical properties of the haloes are briefly discussed. Using the kinematical ages of the haloes and inner nebulae, we conclude that most of the PNe with detected haloes have hydrogen burning central stars.

scholarly journals AGB Mass-Loss History & Haloes Around Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 455-456 ◽  
Author(s):  
Romano L.M. Corradi ◽  
Matthias Steffen ◽  
Detlef Schönberner ◽  
Mario Perinotto
Keyword(s):  
Mass Loss ◽  
Planetary Nebulae ◽  
Common Phenomenon ◽  
Thermal Pulse ◽  
Morphological Basis ◽  
Pulse Cycle

Ionized haloes around planetary nebulae (PNe) are a quite common phenomenon, being found in about 70% of the elliptical PNe for which adequately deep images exist (cf. Corradi, these proceedings). Physically, one has to distinguish between two different kind of haloes. AGB haloes consist of photo-ionized matter still containing information about the mass loss history during the last thermal pulse cycle on the Asymptotic Giant Branch. A second kind of halo may develop when recombination sets in as a consequence of the fast luminosity drop during the advanced post-AGB evolution. These recombination haloes, which can be confused with real AGB haloes on a pure morphological basis, are not a signature of an AGB mass-loss episode (Corradi et al. 2000).

scholarly journals Measuring Mass-Loss Evolution at the Tip of the Asymptotic Giant Branch

2010 ◽  
Vol 27 (2) ◽  
pp. 214-219 ◽  
Author(s):  
C. Sandin ◽  
M. M. Roth ◽  
D. Schönberner
Keyword(s):  
Mass Loss ◽  
Galactic Disk ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Stellar Winds ◽  
Circumstellar Envelope ◽  
Stellar Envelope ◽  
Stellar Properties ◽  
Loss Rates

AbstractIn the final stages of stellar evolution low- to intermediate-mass stars lose their envelope in increasingly massive stellar winds. Such winds affect the interstellar medium and the galactic chemical evolution as well as the circumstellar envelope where planetary nebulae form subsequently. Characteristics of this mass loss depend on both stellar properties and properties of gas and dust in the wind formation region. In this paper we present an approach towards studies of mass loss using both observations and models, focussing on the stage where the stellar envelope is nearly empty of mass. In a recent study we measure the mass-loss evolution, and other properties, of four planetary nebulae in the Galactic disk. Specifically we use the method of integral field spectroscopy on faint halos, which are found outside the much brighter central parts of a planetary nebula. We begin with a brief comparison between our and other observational methods to determine mass-loss rates in order to illustrate how they differ and complement each other. An advantage of our method is that it measures the gas component directly requiring no assumptions of properties of dust in the wind. Thereafter we present our observational approach in more detail in terms of its validity and its assumptions. In the second part of this paper we discuss capabilities and assumptions of current models of stellar winds. We propose and discuss improvements to such models that will allow meaningful comparisons with our observations. Currently the physically most complete models include too little mass in the model domain to permit a formation of winds with as high mass-loss rates as our observations show.

scholarly journals Pre-White Dwarf Evolution: Up to Planetary Nebulae

1989 ◽  
Vol 114 ◽  
pp. 29-43 ◽  
Author(s):  
Italo Mazzitelli
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Planetary Nebulae ◽  
Mass Function ◽  
Theoretical Relation ◽  
Helium Burning ◽  
The Core ◽  
Bona Fide

AbstractThe main evolutionary phases having some interest for the formation of the remnant white dwarf are discussed, starting from the core helium burning phase, in the attempt of evaluating a theoretical relation between initial main sequence mass and final white dwarf mass. Several difficulties, mainly due (but not only) to uncertainties in the theory of mass loss, have been met, so that only a fiducial bona fide correlation can be drawn. The mass function of population I white dwarfs has probably a secondary maximum at M = 0.9 – 1 Me.

scholarly journals Low Mass Wolf-Rayet Stars: Theory

1982 ◽  
Vol 99 ◽  
pp. 413-422 ◽  
Author(s):  
Alvio Renzini
Keyword(s):  
Massive Stars ◽  
Asymptotic Giant Branch ◽  
Intermediate Mass ◽  
Helium Burning ◽  
Hydrogen Burning ◽  
Intermediate Mass Stars ◽  
Low Mass ◽  
Chandrasekhar Limit ◽  
Central Stars ◽  
Evolutionary Product

It is well known that the Wolf-Rayet phenomenon is not restricted to some bright and massive stars, presumably in their core hydrogen-burning or helium-burning phase, but that it is also encountered among the central stars of some planetary nebulae (PNe). The PN nuclei are generally regarded as the evolutionary product of low and intermediate mass stars (with initial masses M.1 below ∼5 M⊙), which have lost most of their hydrogen-rich envelope during the so-called Asymptotic Giant Branch (AGB) phase. Correspondingly, their present mass cannot exceed the Chandrasekhar limit (∼1.4 M⊙), and their internal structure consists of a highly degenerate carbon-oxygen core containing most of the stellar mass, surrounded by an intershell region of mass ΔMCSH, and by a very low-mass envelope (Me < ∼10−3 M⊙).

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